The design of latches for doors has taken a variety of forms, the most common being the horizontal spring bolt which is depressed by the striker plate and then pops into an opening in the striker plate when the door is fully closed. This type of spring latch has a number of disadvantages in that it is difficult to adjust except by repositioning the stop or the striker plate on the jamb, giving rise to the problem of a door which rattles. Unless some positive latching control is used, the spring bolts can be easily wedged or deflected by a wire, plastic card, or other metal devices to permit the door to be opened even though the mechanism controlling the latch is locked. This has given rise to the use of "dead bolt" type latches particularly for outside doors to provide a positive locking action.
Various types of rotary latches have heretofore been proposed, particularly for use with automobile doors where alignment problems and other safety considerations impose special requirements. However, such rotary latch arrangements have generally been too complicated or expensive, or difficult to install to be useful with common household doors. A rotary door latch mechanism, for example, as is described in U.S. Pat. No. 1,711,213 requires the door to close against a stop. It does not provide a flush, smooth external appearance either with the door open or closed, since the keeper requires a striking lip which must project toward the door and requires an exposed opening in the jamb adjacent the door.